Dual layer deduplication for a file system running over a deduplicated block storage

ABSTRACT

An aspect of dual layer deduplication for a file system running over a deduplication block storage system includes accessing a file by a file system driver of the file system. The file is stored as one of a plurality of files in the file system. A further aspect includes breaking the file down into multiple blocks and generating chunks from the blocks. For at least one of the chunks, a trail of zeros is added until a size of a respective one of the chunks is a multiple of a block size of the deduplication block storage system.

BACKGROUND

Data deduplication (also referred to simply as “deduplication”) is aspace-saving technology intended to eliminate redundant (duplicate) data(such as, files) on a data storage system. By saving only one instanceof a file, disk space can be significantly reduced. For example, if afile of size 10 megabytes (MB) is stored in ten folders of each employeein an organization that has ten employees. Thus, 100 megabytes (MB) ofthe disk space is consumed to maintain the same file of size 10megabytes (MB). Deduplication ensures that only one complete copy issaved to a disk. Subsequent copies of the file are only saved asreferences that point to the saved copy, such that end-users still seetheir own files in their respective folders. Similarly, a storage systemmay retain 200 e-mails, each with an attachment of size 1 megabyte (MB).With deduplication, the disk space needed to store each attachment ofsize 1 megabyte (MB) is reduced to just 1 megabyte (MB) from 200megabyte (MB) because deduplication only stores one copy of theattachment.

Data deduplication can operate at a file or a block level. Filededuplication eliminates duplicate files (as in the example above), butblock deduplication processes blocks within a file and saves unique copyof each block. For example, if only a few bytes of a document orpresentation or a file are changed, only the changed blocks are saved.The changes made to few bytes of the document or the presentation or thefile does not constitute an entirely new file.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described herein in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

One aspect may provide a method for dual layer deduplication for a filesystem running over a deduplication block storage system. The methodincludes accessing a file by a file system driver of the file system.The file is stored as one of a plurality of files in the file system.The method further includes breaking the file down into multiple blocksand generating chunks from the blocks. For at least one of the chunks, atrail of zeros is added until a size of a respective one of the chunksis a multiple of a block size of the deduplication block storage system

Another aspect may provide a system for dual layer deduplication for afile system running over a deduplication block storage system. Thesystem includes a memory having computer-executable instructions and aprocessor. The processor executes the computer-executable instructions.When executed by the processor, the computer-executable instructionscause the processor to perform operations. The operations includeaccessing a file by a file system driver of the file system. The file isstored as one of a plurality of files in the file system. The operationsfurther include breaking the file down into multiple blocks andgenerating chunks from the blocks. For at least one of the chunks, atrail of zeros is added until a size of a respective one of the chunksis a multiple of a block size of the deduplication block storage system.

Another aspect may provide a computer program product embodied on anon-transitory computer readable medium. The computer program productincludes instructions that, when executed by a computer, causes thecomputer to perform operations. The operations include accessing a fileby a file system driver of the file system. The file is stored as one ofa plurality of files in the file system. A further aspect includesbreaking the file down into multiple blocks and generating chunks fromthe blocks. For at least one of the chunks, a trail of zeros is addeduntil a size of a respective one of the chunks is a multiple of a blocksize of the deduplication block storage system.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

Objects, aspects, features, and advantages of embodiments disclosedherein will become more fully apparent from the following detaileddescription, the appended claims, and the accompanying drawings in whichlike reference numerals identify similar or identical elements.Reference numerals that are introduced in the specification inassociation with a drawing figure may be repeated in one or moresubsequent figures without additional description in the specificationin order to provide context for other features. For clarity, not everyelement may be labeled in every figure. The drawings are not necessarilyto scale, emphasis instead being placed upon illustrating embodiments,principles, and concepts. The drawings are not meant to limit the scopeof the claims included herewith.

FIG. 1A is a block diagram of a content-based storage system havingmulti-level cache for deduplicated storage;

FIG. 1B illustrates further detail of the system of FIG. 1A;

FIG. 2 is a flow diagram of read and write operations for the system ofFIG. 1A;

FIG. 3 is a block diagram of a content-based storage system having acontrol module with a first cache and a data module with a second cache;

FIG. 4 is a schematic representation of address-to-hash (A2H) mapping ina control module and hash-to-physical (H2P) mapping in a data module fora content-based storage system;

FIG. 5 is a block diagram of a simplified system for implementing duallayer deduplication for a file system running over a deduplication blockstorage system;

FIG. 6 is a block diagram of sample file system blocks;

FIG. 7 is a flow diagram of a process for implementing dual layerdeduplication for a file system running over a deduplication blockstorage system; and

FIG. 8 is a block diagram of an illustrative computer that can performat least a portion of the processing described herein.

DETAILED DESCRIPTION

Before describing embodiments of the concepts, structures, andtechniques sought to be protected herein, some terms are explained. Thefollowing description includes a number of terms for which thedefinitions are generally known in the art. However, the followingglossary definitions are provided to clarify the subsequent descriptionand may be helpful in understanding the specification and claims.

As used herein, the term “storage system” is intended to be broadlyconstrued so as to encompass, for example, private or public cloudcomputing systems for storing data as well as systems for storing datacomprising virtual infrastructure and those not comprising virtualinfrastructure. As used herein, the terms “client,” “host,” and “user”refer, interchangeably, to any person, system, or other entity that usesa storage system to read/write data. In some embodiments, the term“storage device” may also refer to a storage array including multiplestorage devices. In certain embodiments, a storage medium may refer toone or more storage mediums such as a hard drive, a combination of harddrives, flash storage, combinations of flash storage, combinations ofhard drives, flash, and other storage devices, and other types andcombinations of computer readable storage mediums including those yet tobe conceived. A storage medium may also refer both physical and logicalstorage mediums and may include multiple level of virtual to physicalmappings and may be or include an image or disk image. A storage mediummay be computer-readable, and may also be referred to herein as acomputer-readable program medium.

In certain embodiments, the term “I/O request” or simply “I/O” may beused to refer to an input or output request, such as a data read or datawrite request.

In certain embodiments, a storage device may refer to any non-volatilememory (NVM) device, including hard disk drives (HDDs), solid statedrivers (SSDs), flash devices (e.g., NAND flash devices), and similardevices that may be accessed locally and/or remotely (e.g., via astorage attached network (SAN) (also referred to herein as storage arraynetwork (SAN)).

In certain embodiments, a storage array (sometimes referred to as a diskarray) may refer to a data storage system that is used for block-based,file-based or object storage, where storage arrays can include, forexample, dedicated storage hardware that contains spinning hard diskdrives (HDDs), solid-state disk drives, and/or all-flash drives (e.g.,the XtremIO all flash drive, available from DELL/EMC of HopkintonMass.). In certain embodiments, a data storage entity may be any one ormore of a file system, object storage, a virtualized device, a logicalunit, a logical unit number, a logical volume, a logical device, aphysical device, and/or a storage medium.

In certain embodiments, a physical storage unit may be a physicalentity, such as a disk or an array of disks, for storing data in storagelocations that can be accessed by address, where physical storage unitis used interchangeably with physical volume. In certain embodiments, adata storage entity may be any one or more of a file system, objectstorage, a virtualized device, a logical unit, a logical unit number, alogical volume, a logical device, a physical device, and/or a storagemedium.

In certain embodiments, an image may be a copy of a logical storage unitat a specific point in time. In certain embodiments, a clone may be acopy or clone of the image or images, and/or drive or drives of a firstlocation at a second location. In some embodiments, a clone may be madeup of a set of objects.

In certain embodiments, a snapshot may refer to differentialrepresentations of an image, i.e. the snapshot may have pointers to theoriginal volume, and may point to log volumes for changed locations. Incertain embodiments, a snapshot may refer to differentialrepresentations of the state of a system. Snapshots may be combined intoa snapshot array, which may represent different images over a timeperiod or different states of a system over a time period.

In certain embodiments, a journal may be a record of write transactions(e.g., I/O data) issued to a storage system, which may be used tomaintain a duplicate storage system, and to roll back the duplicatestorage system to a previous point in time. In some embodiments, eachentry in a journal contains, apart from the I/O data itself, I/Ometadata that can include information such as a volume identifier (ID),the I/O block offset within the volume, the I/O length, and a time stampof the I/O.

In certain embodiments, XtremIO, available from Dell EMC of Hopkinton,Mass.) is a type of content addressable storage array that uses allflash technology. Flash, as is understood, is a solid-state (SS) randomaccess media type that can read any address range with no latencypenalty, in comparison to a hard disk drive (HDD) which has physicalmoving components which require relocation when reading from differentaddress ranges and thus significantly increasing the latency for randomI/O data.

In certain embodiments, an X-page is a predetermined-size aligned chunkas the base unit for memory and disk operations. In certain embodimentsdescribed in the present description, the X-Page size is referred to ashaving 4 KB; however other smaller or larger values can be used as well,and nothing in the design is limited to a specific value.

In certain embodiments, a logical X-page address is the logical addressof an X-page, containing a LUN identifier as well as the offset of theX-page within the LUN.

In certain embodiments, a data protection strategy that can beadvantageous for use with computer systems, especially networked storagesystems, is checkpointing. A checkpoint, as used herein, contains aconsistent point in time image of an entire system, includingconfiguration, logical volume mapping metadata, physical on disk layoutmetadata, and actual user data. In certain embodiments, a checkpointpreserves the state of a system at a given point in time by saving oneor more snapshots of, for example, a file system, or an application atone or more points in time. A checkpoint can preserve a snapshot of anapplication's state, so that it can restart from that point in case offailure, which can be useful for long running applications that areexecuted in failure-prone computing systems. If a checkpoint is used, anapplication periodically writes large volumes of snapshot data topersistent storage in an attempt to capture its current state. Thus, ifthere is a failure, the application can recover by rolling-back itsexecution state to a previously saved checkpoint.

In certain embodiments, a “checkpoint” refers at least to an entitycreated by a checkpoint process, where the checkpoint process performsactions to preserve the state of an apparatus, system, or other entity(including software entities) at a particular time. Advantageously, acheckpoint includes information such as user data, the configuration ofthe apparatus, user metadata, and other information related to theinternal state of the apparatus or system. For example, some storagesystems (including XtremIO), in accordance with certain embodimentsherein, also provide some kind of checkpoint feature, to provide anability to preserve system state including user data and metadata atsome defined point in time in order to restore this state after systemmalfunction or corruption. In certain embodiments, the checkpointcorresponds to a frozen, immutable re representation of the state of asystem or apparatus at certain point in time, including user data,metadata, and the system configuration. In certain embodiments, thecheckpoint is stored in a dedicated, reserved location within thesystem. In certain embodiments, the checkpoint is able to be created inan online, dynamic environment, where the checkpoint creation istransparent to entities having I/O interactions with the system.

For a file system, the accuracy and consistency of a file system isnecessary to relate applications and data, so a checkpoint provides away to provide periodic backup of file server state to allow systemrecovery in the event of faults or failures. When data corruption isdetected, one of the checkpoints can be used for file system recovery.Similarly, a checkpoint, in a virtualization context, is a snapshot ofthe state of a virtual machine. Like a restore point in MICROSOFTWINDOWS operating systems, a checkpoint allows an administrator torestore an entity (e.g., a computer system, a file system, anapplication, a virtual machine, etc.) to a previous state. Checkpointsalso can be used to create backups before conducting updates. Should anupdate fail or cause problems, an administrator can return the virtualmachine to its state prior to the update. A recover action is used toreturn the system to the checkpoint state.

It is envisioned that at least some embodiments herein are usable withone or more of the embodiments described in certain commonly owned U.S.patents, including: U.S. Pat. No. 8,990,495 (“Method and System forStoring Data in RAID Memory Devices”); U.S. Pat. No. 9,104,326(“Scalable Block Data Storage Using Content Addressing”) (hereinafter“'326 patent”); and U.S. Pat. No. 9,606,870 (“Data Reduction Techniquesin a Flash-Based Key/Value Cluster Storage”), each of which is herebyincorporated by reference.

While vendor-specific terminology may be used herein to facilitateunderstanding, it is understood that the concepts, techniques, andstructures sought to be protected herein are not limited to use with anyspecific commercial products. In addition, to ensure clarity in thedisclosure, well-understood methods, procedures, circuits, components,and products are not described in detail herein.

The phrases, “such as,” “for example,” “e.g.,” “exemplary,” and variantsthereof, are used herein to describe non-limiting embodiments and areused herein to mean “serving as an example, instance, or illustration.”Any embodiments herein described via these phrases and/or variants isnot necessarily to be construed as preferred or advantageous over otherembodiments and/or to exclude the incorporation of features from otherembodiments. In addition, the word “optionally” is used herein to meanthat a feature or process, etc., is provided in some embodiments and notprovided in other embodiments.” Any particular embodiment of theinvention may include a plurality of “optional” features unless suchfeatures conflict.

FIG. 1A shows an illustrative content-based data storage system 100 withdeduplication that may have multi-level data caches in accordance withembodiments of the disclosure. In the illustrated embodiment, first,second, third, and fourth nodes 102, 104, 106, 108 can be interconnectedby a switch 110 via a switch interface 111. The first node 102 caninclude a control system 114 and a data system 116. In embodiments,separate data and control planes may be provided by the control and datasystems 114, 116. The control system 114 may control execution of readand write commands to the storage devices 112. The data systems 116 maybe connected to the storage devices 112 and, under control of arespective control system 114, may pass data to and/or from the storagedevices via suitable storage drivers 113.

The data and/or control systems 114, 116 may retain extracts of the datastored in the storage devices 112. In embodiments, the data extracts maybe generated by cryptographic hashing of the data content in the datablocks. In embodiments, the extracts may be used for content addressingof the data blocks to the physical storage devices 112.

The second node 104 can include a hash system 117 to generate thehash/extract, which can be referred to as a content fingerprint for thedata blocks. The second node 104 can also include a routing system 118,along with a switch interface 111 and a SAN interface 115. The routingsystem 118 may terminate storage and retrieval operations and distributecommands to control systems 114 that may be selected for the operationin such a way as to retain balanced usage within the system. In theillustrated embodiment, the third node 106 can be similar to the firstnode 102 and the fourth node 108 can be similar to the second node 108.

The routing systems 118 may use the hash values calculated from datablocks to select control systems 114 for distribution. Moreparticularly, selection of the control system 114 may use hash values,or may rely on the user address and not on the content (hash). The hashvalue may, however, be used for selecting the data system 116, and forsetting the physical location for data storage within the data system.

In example embodiments, control modules 114 can include a C cache 115and the data modules 116 can include a D cache 117. As explained morefully below, the C cache 115 can include addresses, address hashes, andphysical data location information and the D cache 117 can include, foreach bucket, a filter, a hash to address, and bucket information.

In some examples, the system 100 may employ more than a single type ofmemory technology, including a mix of more than one Flash technology(e.g., single level cell (SLC) flash and multilevel cell (MLC) flash),and a mix of Flash and DRAM technologies. In certain embodiments, datamapping may optimize performance and life span by taking advantage ofthe different access speeds and different write/erase cycle limitationsof the various memory technologies.

FIG. 1B is an example of a system that can include a hash system 150communicatively coupled to a routing system 152, which can becommunicatively coupled to a control system 154 and a data system 156.The data system 156 can be communicatively coupled to any practicalnumber of memory devices 158. The routing system 152 can routeread/write commands from a host (not shown) to control and data systems154, 156 for execution. In embodiments, the data content-based mappingto physical storage 158 can distribute workload relatively evenly andprovide separation of the control and data paths. Read and writeoperations to the SSDs 158 can be used to generate priority values forthe data blocks, as described more fully below.

FIG. 2 shows an example IO operation. A host 217 may issue a readcommand for a logical block address, which is shown as address “6,” viaa Fibre Channel or iSCSI port, for example. The routing system 218 mayreceive the read command and determine a requested address range in datablocks of 4K, for example, and pass the address information to thecontrol system 214. The control system 214 may look up address 6 toobtain the hash value, which is shown as H6. This may be referred to asaddress-to-hash (A2H) lookup. The H6 hash value may be passed to thedata system 216 which can perform a look up of the H6 hash value in ahash-to-physical address (H2P) table to read the physical address forthe data. In the example, the physical address is shown as “G.” The datasystem 216 can use the physical address to read the data block (DB) atphysical address Gin the SSD 221. A reference count can correspond to anumber of times the hash value is referenced in physical storage. Inembodiments, write reference information can be modified for each uniqueand/or deduplicated write and access reference information can bemodified for each read and/or write access.

For a write operation from a host, the routing system 218 can receivethe write data and can segment the data stream into data blocks andgenerate hash values for the data blocks. The hash value can be providedto the control system 214 to determine if the write data is unique. Ifunique, the hash value can be placed in an address mapping. The controlsystem 214 can pass the hash value to the data system 216, which canassign the hash value to a physical address and write the data block(s)to the SSD at the physical address. In embodiments, the write referenceinformation and/or the access reference information, can be modified,e.g., incremented,

If the hash value generated by the routing system 218 is not unique, thecontrol system 214 can determine that data already exists at thephysical address for the hash value. Since the data already exists, thedata system 216 can increment the write reference information for thedata block. In embodiments, the access reference information can also bemodified. The data may not be written to the SSD. Deduplication mayrefer to a write operation where a hash for a data block is found not beunique and the non-unique data block is not written to physical storage.The reference count for the non-unique hash may be incremented.

FIG. 3 shows a storage system 300 according to an illustrativeembodiment of the disclosure. The storage system 300 may be the same asor similar to a node within the distributed storage system of FIG. 1A.The storage system 300 may include a plurality of modules 302 a-302 d(generally denoted 302 herein), a storage array 306 comprising aplurality of storage devices 308 a . . . 308 n (generally denoted 308herein), and a primary memory 318. In some embodiments, the storagedevices 308 may be provided as solid-state devices (SSDs).

As described further herein, the storage system 300 also can include a C(also called logical) cache 317 and a D (also called physical) cache323. The C cache 317 and/or the D cache 323 can, in certain embodiments,be physical devices configured to store certain data so that futurerequests for that data can be served faster. Although the C cache 317and D cache 323 are shown as being part of the storage system, it isunderstood that the C cache 317 and/or D cache 323 can be locatedanywhere such that they are accessible quickly to the storage system.Data that is stored within a cache might include data values that havebeen computed earlier or duplicates of original values that are storedelsewhere. If the requested data is contained in the cache (hereinreferred to as a cache hit), this request can be served by simplyreading the cache, which is comparatively faster than going to othertypes of memory. On the other hand, if the requested data is notcontained in the cache (herein referred to as a cache miss), the datamay have to be to be recomputed or fetched from its original storagelocation, which is comparatively slower. Hence, the greater the numberof requests that can be served from the cache, the faster the overallsystem performance becomes.

The primary memory 318 can be any type of memory having access timesthat are faster compared to the storage devices 308. In someembodiments, primary memory 318 may be provided as dynamic random-accessmemory (DRAM). In certain embodiments, primary memory 318 may beprovided as synchronous DRAM (SDRAM). In one embodiment, primary memory318 may be provided as double data rate SDRAM (DDR SDRAM), such as DDR3SDRAM.

As described above, the control subsystem 302 b may be configured tomaintain a mapping between I/O addresses associated with data and thecorresponding chunk hashes. As shown in FIG. 3, this mapping may bemaintained using a data structure 312, referred to herein as an “I/Oaddress to chunk hash mapping table” or “A2H table,” (also known as A→Htable) according to some embodiments. In one embodiment, I/O addressesmay be logical addresses used by clients 320 to access data within thestorage system 300.

As also described above, the data subsystem 302 c may be configured tomaintain a mapping between chunk hashes and physical storage addresses(i.e., storage locations within the storage array 306 and/or withinindividual storage devices 308). This mapping may be maintained using adata structure 314, referred to herein as a “hash to physical addressmapping table” or “H2P table,” or “H→P table,” according to someembodiments, where this table, in certain embodiments, includesinformation similar to that of the aforementioned HMD (hash metadata)and PL (physical layout) tables. In certain embodiments, as described,for example, in the incorporated by reference patents, there also may bea mapping referred to as the H2D or H→D table, where D stands for diskphysical layout. In certain embodiments, the H2P table is maintained toroute data with different hashes to different D modules. The datasubsystem 302 c may be also be configured to read and write data from/tothe storage array 306 (and/or to individual storage devices 308therein).

As described above, in a content addressable storage system, data isstored in blocks, for example 16 KB, 8 KB, 4 KB, etc., where each blockhas a universally unique large hash signature, for example of 20 bytes,which can be saved to disk, e.g., Flash memory. As described herein,hash signatures may be accessed by small in-memory handles (referred toherein as short hash handles, hash handles, or short hashes), forexample of 6 bytes. These short hashes may be unique to eachvolume/array, but not necessarily unique across volumes/arrays.Additional information relating to hash-based replication, computationof hashes, generation and use of short hash handles can be found in U.S.Pat. No. 9,378,106 (“Hash Based Replication”); U.S. Pat. No. 9,208,162(“Generating a Short Hash Handle”) and U.S. Pat. No. 9,396,243(“Hash-Based Replication Using Short Hash Handle and Identity Bit”),each of which is hereby incorporated by reference.

In embodiments, address to hash mapping (A2H) maps an address inside avolume to the short hash value of its data. In embodiments, meta datacan include for each address the hash value of the content. If the basisfor deduplication is 16 KB, then the meta data holds for each addressthe short hash value of the data to which the address points. In caseswhere access to the volume is in larger chunks than the size of thebasic hash value, the meta data for the address space can be readilycached.

As also noted above, hash to physical disk locations can include foreach hash key (e.g., 6 bytes) the location on the disk, and thereference count. Where a storage system uses hash keys of 6 bytes, theremay be collisions of data generating the same hash. If there is acollision, a new hash key from a different hash address space isgenerated for the data when the data is written. This means that thehash to physical disk location table may search for a hash value everytime a new write arrives. If the write has the same hash value, there isa need to check the long hash value, and verify if there is a hashcollision, or whether it is actually the same data. This means thatduring every write if the hash to physical disk location table is not inthe system memory, there may a need to fetch the meta data of the hashfrom the disk to verify if such a hash exists. It will be appreciatedthat meta data structures may consume most of system memory, e.g., DRAM,in the storage system, so that the meta data limits the total size ofthe storage system.

FIG. 4 shows an example control or C module address to hash (A2H)mapping 400. As can be seen, as data blocks arrive, the content for theaddress is hashed to generate H1, H2, H3, H4, H5, as shown. It should benoted that H1 appears twice and is deduplicated. The D-module includes ahash to physical (H2P) mapping showing the physical offset of the dataalong with a reference count indicative of how many times a given hashvalue occurs. It will be appreciated that a particular hash value havinga high reference count will likely be accessed more often than hashvalues having a low reference count. In embodiments, a reference countis incremented each time the hash value is generated in a volume. Thus,higher reference count hash values may be preferred for placement in Dcache over low reference count hash values. It can be seen that thephysical offset corresponds to the order in which a unique hash value isgenerated. For example, H3 is shown with an offset value of 2 since asecond H1 value was deduplicated.

Modern storage systems, such as XtremIO, leverage flash drives toprovide fast reliable de-duplicated storage. One of the challenges of ablock based inline deduplication storage system is the fact that theyuse block aligned deduplication, which is less effective than bytealigned de duplication used by secondary storage arrays like datadomain. For block storage it is more difficult to create byte aligneddeduplication as IOs arrive in blocks, and it is hard to chunk the datacorrectly compared to a file system. Chunking refers to a process ofsplitting a file into pieces called chunks. In data deduplicationapplications, the process of chunking facilitates duplicate detectionperformance of the system.

A deduplication storage system, such as XtremIO has two layers foraccessing the volume data. As described above, there is a layer mappingfrom address in the volume to the hash value of the data, and a secondlayer mapping from the hash value to a location on the disk. The addressto hash mapping maps an address inside a volume to the hash value of itsdata. The metadata includes for each address the hash value of thecontent. If the basic use of deduplication is 16 KB, then the metadataholds for each address the short hash value (6 bytes) of the data theaddress points to. In many cases, access to the volume is in largerchunks than the size of the basic hash value. This means that themetadata for the address space can be easily cached, and standardprefetching algorithms work efficiently.

The hash to physical disk location includes for each hash key (6 bytes)the location on the disk and the reference count. Since the system isarchitected to keep hash keys of 6 bytes, there may be collision of datagenerating the same hash, if there is a collision a new hash key from adifferent hash address space is generated for that data, when the datais written. This means that the hash to physical disk location table,must search for a hash value every time a new write arrives, if thewrite has the same hash value, there is a need to check the long hashvalue, and verify if there is a hash collision, or it is actually thesame data. This means that during every write if the table is not in thesystem memory, there is a need to fetch the meta data of the hash fromthe disk and verify if such hash exists.

Many systems today use a file system over the block devices that a blockstorage exposes. A file system element is a file which is mapped to alist of blocks. In many cases there are files having many parts of databeing identical. One good example is a large customer that generatesvery large video files, and the files are identical except that eachvideo has embedded subtitles which are part of the video. As there maybe many countries to which the high quality video is targeted, thismeans that there is a lot of duplications in the data. The differencesin the subtitles cause a drift in the block alignment between the videoresulting in little or no deduplication. A byte aligned deduplicationsystem can manage such assignment problems much better than block leveldeduplication and achieve effective deduplication ratios.

Block aligned deduplication systems typically support compression, whichmeans trailing zeros will have little impact.

Embodiments described herein provide a dual-level deduplication system.In certain cases, an enterprise can utilize different types of storagesystems to form a complete data storage environment. In one arrangement,the enterprise can utilize both a block based storage system and a filebased storage hardware, such as a VNX™ or VNXe™ system (produced by EMCCorporation, Hopkinton, Mass.). In such an arrangement, typically thefile based storage hardware operates as a front-end to the block basedstorage system such that the file based storage hardware and the blockbased storage system form a unified storage system.

Turning now to FIG. 5, the system 500 includes a file system 502communicatively coupled to a backend deduplication block storage system504. The file system 502 includes a file system driver 506, whichcreates a modified representation of its files. This modifiedrepresentation of the files enables the backend deduplication system 504to have a higher deduplication ratio, with minor performance effect.

The file system driver 506 may run on in any file system that utilizesthe deduplicated block storage system 504 as a background storage. Thefile system 502 includes a number of files 508. Each of the files 508 inthe file system has two parts: the file data (file contents) 510 and themetadata 512 describing the file structure of the respective file.

Each original file is chunked into multiple pieces (portions) 514 usinga variable length chunking algorithm, which may be byte aligned. It isunderstood that the variable length chunking algorithm can bealternatively bit aligned. At the end of each chunk the system will puttrailing zeros until the end of the block (i.e., pad with block untilthe size of the chunk is a multiple of the block size of thededuplicated block storage), e.g., in XtremIO the deduplicated blockstorage is 16 KB. The metadata 512 for each file will include the listof locations where the file was chunked.

The chunk size for files can be larger than the chunks for the blockdeduplication to allow smaller metadata files. Since the chunkingalgorithm is deterministic, the system can verify if a location is aplace for chunking without the metadata indicating this. However, themetadata is needed to be able to access the file randomly.

The modified file system driver 506 will hide the metadata file andallow access only to the data files, leveraging the metadata files toallow random access. The block storage will have correct alignment ofthe data in the blocks, and the effect of the trailing zeros will beminimal on the space as compression, such as run-length encoding (RLE)and Lempel Ziv (LZ) will reduce the space used by the relevant blocks.

An example technique for two data files 602 and 608 is shown in FIG. 6.The example shown in FIG. 6 assumes that a block size is fourcharacters. Turning to FIG. 6, the first file 602 is broken down intosix blocks 604 (four characters each). The second file 608 is brokendown into six blocks 610, also having four characters per block.

The deduplication ratio will be zero, but if chunked correctly and zerosare added in the proper place, the deduplication will be more effective.

The first file 602 will result in chunked blocks 606 having regularblock alignment (i.e., no change from the blocks 604). The second file608 will result in chunked blocks 612. The block storage will notdeduplicate between ABCD ABCZ and D000 but the rest of the data will bededuplicated, and the three zeros added after the ‘D’ will beeffectively compressed.

Turning now to FIG. 7, a flow diagram of a process 700 for implementingthe embodiments herein will now be described. In block 702, the process700 accesses a file in the file system. This may be implemented by thefile system driver. In block 704, the process 700 breaks the file downinto multiple blocks. This step may be implemented by the file systemdriver.

In block 706, the process 700 chunks the blocks. At the end of eachblock the process 700 adds trailing zeros until the size of the chunk isa multiple of a block size of the deduplication block storage. This stepmay be implemented by the file system driver via a variable lengthchunking algorithm. The resulting chunked files may be stored in thefile system.

FIG. 8 shows an exemplary computer 800 (e.g., physical or virtual) thatcan perform at least part of the processing described herein. Thecomputer 800 includes a processor 802, a volatile memory 804, anon-volatile memory 806 (e.g., hard disk or flash), an output device 807and a graphical user interface (GUI) 808 (e.g., a mouse, a keyboard, adisplay, for example). The non-volatile memory 806 stores computerinstructions 812, an operating system 816 and data 818. In one example,the computer instructions 812 are executed by the processor 802 out ofvolatile memory 804. In one embodiment, an article 820 comprisesnon-transitory computer-readable instructions.

Processing may be implemented in hardware, software, or a combination ofthe two. Processing may be implemented in computer programs executed onprogrammable computers/machines that each includes a processor, astorage medium or other article of manufacture that is readable by theprocessor (including volatile and non-volatile memory and/or storageelements), at least one input device, and one or more output devices.Program code may be applied to data entered using an input device toperform processing and to generate output information.

The system can perform processing, at least in part, via a computerprogram product, (e.g., in a machine-readable storage device), forexecution by, or to control the operation of, data processing apparatus(e.g., a programmable processor, a computer, or multiple computers).Each such program may be implemented in a high level procedural orobject-oriented programming language to communicate with a computersystem. However, the programs may be implemented in assembly or machinelanguage. The language may be a compiled or an interpreted language andit may be deployed in any form, including as a stand-alone program or asa module, component, subroutine, or other unit suitable for use in acomputing environment. A computer program may be deployed to be executedon one computer or on multiple computers at one site or distributedacross multiple sites and interconnected by a communication network. Acomputer program may be stored on a storage medium or device (e.g.,CD-ROM, hard disk, or magnetic diskette) that is readable by a generalor special purpose programmable computer for configuring and operatingthe computer when the storage medium or device is read by the computer.Processing may also be implemented as a machine-readable storage medium,configured with a computer program, where upon execution, instructionsin the computer program cause the computer to operate.

Processing may be performed by one or more programmable processorsexecuting one or more computer programs to perform the functions of thesystem. All or part of the system may be implemented as, special purposelogic circuitry (e.g., an FPGA (field programmable gate array) and/or anASIC (application-specific integrated circuit)).

Having described exemplary embodiments of the invention, it will nowbecome apparent to one of ordinary skill in the art that otherembodiments incorporating their concepts may also be used. Theembodiments contained herein should not be limited to disclosedembodiments but rather should be limited only by the spirit and scope ofthe appended claims. All publications and references cited herein areexpressly incorporated herein by reference in their entirety.

Elements of different embodiments described herein may be combined toform other embodiments not specifically set forth above. Variouselements, which are described in the context of a single embodiment, mayalso be provided separately or in any suitable subcombination. Otherembodiments not specifically described herein are also within the scopeof the following claims.

What is claimed is:
 1. A method for dual layer deduplication for a filesystem running over a deduplication block storage system, comprising:accessing a file by a file system driver of the file system, the filestored as one of a plurality of files in the file system; breaking thefile down into multiple blocks; and generating chunks from the blocks,wherein for at least one of the chunks adding a trail of zeros until asize of a respective one of the chunks is a multiple of a block size ofthe deduplication block storage system.
 2. The method of claim 1,wherein the file includes data and metadata describing a structure ofthe data.
 3. The method of claim 2, wherein the metadata for each fileincludes a list of locations where the file is chunked.
 4. The method ofclaim 1, wherein the generating chunks is performed by a variable lengthchunking algorithm.
 5. The method of claim 1, wherein the chunks are oneof byte aligned and bit aligned.
 6. The method of claim 1, wherein achunk size for the files is greater than a chunk size for the blockdeduplication.
 7. The method of claim 1, wherein each of the blocks hasan equal number of characters.
 8. A system for dual layer deduplicationfor a file system running over a deduplication block storage system,comprising: a memory comprising computer-executable instructions; and aprocessor executing the computer-executable instructions, thecomputer-executable instructions when executed by the processor causethe processor to perform operations comprising: accessing a file by afile system driver of the file system, the file stored as one of aplurality of files in the file system; breaking the file down intomultiple blocks; and generating chunks from the blocks, wherein for atleast one of the chunks adding a trail of zeros until a size of arespective one of the chunks is a multiple of a block size of thededuplication block storage system.
 9. The system of claim 8, whereinthe file includes data and metadata describing a structure of the data.10. The system of claim 9, wherein the metadata for each file includes alist of locations where the file is chunked.
 11. The system of claim 8,wherein the generating chunks is performed by a variable length chunkingalgorithm.
 12. The system of claim 8, wherein the chunks are one of bytealigned and bit aligned.
 13. The system of claim 8, wherein a chunk sizefor the files is greater than a chunk size for the block deduplication.14. The system of claim 8, wherein each of the blocks has an equalnumber of characters.
 15. A computer program product embodied on anon-transitory computer readable medium, the computer program productincluding instructions that, when executed by a computer causes thecomputer to perform operations comprising: accessing a file by a filesystem driver of the file system, the file stored as one of a pluralityof files in the file system; breaking the file down into multipleblocks; and generating chunks from the blocks, wherein for at least oneof the chunks adding a trail of zeros until a size of a respective oneof the chunks is a multiple of a block size of the deduplication blockstorage system.
 16. The computer program product of claim 15, whereinthe file includes data and metadata describing a structure of the data.17. The computer program product of claim 16, wherein the metadata foreach file includes a list of locations where the file is chunked. 18.The computer program product of claim 15, wherein the generating chunksis performed by a variable length chunking algorithm.
 19. The computerprogram product of claim 15, wherein the chunks are one of byte alignedand bit aligned.
 20. The computer program product of claim 1, wherein achunk size for the files is greater than a chunk size for the blockdeduplication, and wherein each of the blocks has an equal number ofcharacters.